In recent times, gas-permeable refractory bodies generally described as purge bricks or purge plugs have increasingly been used to introduce various gases into metallurgical furnaces and vessels through their lining for the treatment of molten metals. Such purge bricks are provided particularly in converters for refining hot metal, in hot metal ladles, in foundry ladles and in tundishes used in the continuous casting of steel. Generally, the purge bricks are provided in the bottom of these vessels; however, they may also be incorporated into the lining of the side walls of all such units as well as of other metallurgical furnaces and vessels, such as electric arc furnaces or vessels for treating non-ferrous metals, e.g., aluminum melting furnaces.
Purge bricks may have an increased normal porosity, i.e., bricks having a high number of randomly distributed pores, or a so-called directed porosity or directed pores, i.e., bricks through which a number of pores extend continuously in a desired direction. An advantage of bricks having a directed porosity is that fine-grained solids entrained in gases can be blown through the directed pores, if desired.
Purge bricks of the kind usually employed have often the disadvantage that their durability is lower than that of the refractory lining provided in the furnace or vessel adjacent to the purge bricks. This results in the premature wear of the purge bricks which necessitates a shutdown of the furnace or vessel for repair. For this reason various attempts have been made to improve the durability of purge bricks. Purge bricks in most cases are arranged in an opening or within a perforated brick in the vessel lining. Known apparatus including purge bricks includes a purge brick covered with sheet metal on its side walls and bottom surface. Gas is introduced to the pores in the brick and thereby into the vessel interior through a spiral pipe embedded in the refractory (French Application 24 51 945). The spiral pipe is intended to effect a solidification of molten metal which has entered the purge brick because of wear or cracking and/or which has entered the purge brick or between the purge brick and the opening in which the purge brick is placed because the sheet metal covering of the purge brick has been damaged. In this manner, flow of molten metal out of the vessel is prevented.
A major disadvantage of this purge brick assembly is that it is not easily replaced and consequently relatively long interruptions of the operation of the furnace or vessel will be necessary. Another known purge brick assembly is disposed in an opening in a refractory lining and is provided with a gas supply pipe that is not directly connected to the purge brick of the assembly but connected to an optionally spiral-shaped pipe coil. The coil is connected to the purge brick and embedded either in the purge brick itself or in a refractory body consisting of a refractory block disposed under the purge brick (German Application 31 10 204). A breakthrough of metal cannot reliably be prevented with this design. A substantial improvement is achieved by the use of purge bricks which at the end remote from the interior of the furnace or vessel rest on a safety block. The supply of gas is provided by a system including a partly vertically extending, double pipe coil that is embedded in the safety block (European Patent Application 105,868). The increased surface area resulting from the double pipe coil increases the solidification rate of molten metal entering the system from the vessel.